Patent Document 1 discloses a conventional ceiling-embedded ventilation fan, wherein the fan is connected to a duct placed in a ceiling to communicate with an outdoor environment and is mounted in an embedded manner in the ceiling. FIG. 9 is a sectional view of the ceiling-embedded ventilation fan mounted in the ceiling.
As illustrated in FIG. 9, the ceiling-embedded ventilation fan has frame 104 having a box shape, adapter 106, casing 108, centrifugal blower blade 109, and electric motor 110. Box-shape frame 104 is provided with intake port 102 covered with grille 101 formed in a lower face thereof, and discharge port 103 formed in a side face thereof. Duct 105, which communicates with the outdoor environment, is connected to adapter 106. Casing 108 has a scroll shape having orifice 107 used as an intake port in an interior lower face of frame 104. Centrifugal blower blade 109 is housed in casing 108 to blow air. Electric motor 110 rotates centrifugal blower blade 109.
The conventional ceiling-embedded ventilation fan having the above configuration involves a larger resistance loss, reducing an airflow in the event that some parts of duct 105 are inflected when placed in the ceiling or duct 105 is longer than expected. When using the ceiling-embedded ventilation fan under such an increased resistance loss resulting in a large static pressure, a product specification focusing on the intensity of airflow makes it necessary to increase the outer circumferential speed of an impeller provided in centrifugal blower blade 109. To increase the outer circumferential speed, it becomes necessary to increase the number of rotations of electric motor 110, thus problematically increasing a noise value.
The product specification focusing on the intensity of airflow when the static pressure is high leads to another problem that there is less airflow when the static pressure is low.